Add physics methods to queue and apply movements
Apply movement by queueing it to do later
Improve movement inertia

Handles all 3 axis. Incoming velocity is only added to inertia when
leaving the ground, and does not continually add to it.
Improve mid-air control
Some physics cleanup

Gets rid of some unneeded/unused variables, and halves the 'on ground'
offset.
Implement a jumping state
Fix tracing down
Better handle animations with a 0-length loop
Improve stepping down when starting on the ground
Implement jumping animations
Don't start the jump animation until after the actor is airborn

A bit counter-intuitive, but otherwise certain jump animations will improperly
add an offset to the initial inertia.
Add NPC landing sounds for soundgen keys
Fix a potential divide-by-zero
Continually add bits of input velocity to inertia when falling
Merge remote-tracking branch 'zini/master' into physics
Increase the max number of physics iterations

Should help with highly tessellated collision meshes with high
framerates.
Merge remote-tracking branch 'zini/master' into physics
Don't update player physics more than 60 times a second

Bullet and/or our collision handling code doesn't like timesteps much
smaller than that. Ideally we should do physics in 60fps (or even 30fps)
steps and use prediction and interpolation to get more, but that's not
straight forward and needs a fixed timestep loop to lock physics and
logic together.